A pressurization device is fitted to vehicle tanks in order to maintain a given level of pressure inside the tank itself. Such a device is usually characterised by having a unidirectional valve which is normally closed and is configured to open when the pressure inside the tank reaches a specified threshold. When the valve opens, it allows the outflow of a certain volume of air and/or fuel vapours to the atmosphere, optionally passing through a canister to recover the vapours.
The valve has a valve seat and a shutter which can move towards and away from the valve seat and, in some solutions, has a weight whose magnitude determines the operation of closure and, therefore, the aforesaid pressure threshold. It may also be provided with a set point spring with a relatively low preload, in order to keep the shutter closed against the valve seat despite the vehicle's jolts and vibrations in normal driving condition, and/or in order to increase the value of the threshold pressure required to move the shutter.
In known solutions, the shutter has difficulty in fully lifting from the valve seat and in quickly bringing the internal conditions of the tank below the established threshold pressure, especially when the pressure in the tank slightly exceeds this threshold.